The proposed study seeks to develop and validate a clinical prediction rule for post-coronary artery bypass grafting (CABG) atrial fibrillation and atrial flutter (AF). These arrhythmias occur in 20-40% of the 500,000 patients undergoing CABG, and increase the morbidity, cost, and length of stay associated with the procedure. Though several studies have suggested that prophylactic therapy with beta-adrenergic blockers decreases the risk of post-CABG AF, this efficacy has not been universally appreciated. As a result, several new prophylactic therapies have been introduced, though some with significant toxicities associated with them. It is therefore imperative to identify a priori those individuals most at risk of developing post-CABG AF, as well as those unlikely to develop this endpoint. In this manner, those individuals most at risk of developing post-CABG AF may be targeted for prophylactic therapy, while those in a low risk category may be spared the exposure to a potentially deleterious therapy from which they are less likely to derive benefit. Additionally, the identification of a high-risk subgroup would allow for the execution of smaller randomized controlled trials, and may provide insight into the etiology of post-CABG AF. The study is a retrospective cohort study designed to identify pre-, intra-, and post-operative variables which may be associated with post-CABG AF. From these results, a clinical prediction rule will be formulated. Validation of the prediction rule will then take place in a prospective cohort study using a different group of patients from which the rule was derived. This will allow for the assessment of both validity and generalizability. The candidate has committed himself to a career as an independent investigator, with an interest in the application of rigorous epidemiologic techniques to questions of importance in cardiac electrophysiology, his area of clinical expertise. This project will be an integral part of the candidate?s career development plan and his maturation as an epidemiologist, cardiac electrophysiologist, and clinical investigator.